While, largely in the context of terrestrial optical communications at currently favored wavelengths in the vicinity of 1 micrometer, devices for the detection and modulation of visible and near-visible electromagnetic radiation have evolved rapidly, the field of infrared devices has remained relatively less well-developed. Practical long-wave infrared detection devices have been based on opto-electronic activity in materials such as mercury-cadmium telluride or doped silicon, quantum-well detectors using compound semiconductor materials having received mostly theoretical attention. Representative reports concerning the latter are cited as follows:
D. D. Coon et al., "New mode of IR Detection Using Quantum Wells", Applied Physics Letters, Vol. 45 (1984), pp. 649-651, disclosing infrared radiation detection as based on charge-depletion in localized impurity levels in semiconductors to which an electric field is applied, charge-depletion taking the form of photoemission from a single Al.sub.x Ga.sub.1-x As/GaAs/Al.sub.y Ga.sub.1-y As symmetric quantum well;
J. S. Smith et al., "A New Infrared Detector Using Electron Emission from Multiple Quantum Wells", Journal of Vacuum Science and Technology, Vol. B1 (1983), pp. 376-378, disclosing the use of a plurality of GaAs/GaAlAs quantum wells from which electrons are ejected upon excitation by free-carrier absorption--see also U.S. Pat. No. 4,620,214, issued Oct. 28, 1986 to S. Margalit et al.; and
L. Esaki et al., "New Photoconductor", IBM Technical Disclosure Bulletin, Vol. 20 (1977), pp. 2456-2457, disclosing a superlattice structure in which electrons in the lowest sub-band of quantum wells are essentially immobile, while electrons in a second sub-band have significant mobility.
Typically also, proposals have been made as predicated on photonic excitation of electrons from the valence band to the conduction band, the following being cited further as representative in this respect:
U.S. Pat. No. 4,525,731, issued Jun. 25, 1985 to T. I. Chappel et al.; U.S. Pat. No. 4,439,782, issued Mar. 27, 1984 to N. Holonyak; U.S. Pat. No. 4,607,272, issued Aug. 19, 1986 to G. C. Osbourn; U.S. Pat. No. 4,450,463, issued May 22, 1984 to R. Chin; and F. Capasso et al., "New Avalanche Multiplication Phenomenon in Quantum-well Superlattices: Evidence of Impact Ionization Across the Band-edge Discontinuity", Applied Physics Letters, Vol. 48 (1986), pp. 1294-1296.
A detector based on the generation of photoelectrons by resonant intersubband absorption and tunneling has been disclosed by B. F. Levine et al., "Quantum-well Avalanche Multiplication Initiated by 10-.mu.m Intersubband Absorption and Photoexcited Tunneling", Applied Physics Letters, Vol. 51 (1987), pp. 934-936. The invention as described below is motivated by the desire to provide for increased efficiency in the collection of photocarriers while, simultaneously, dark-current is kept low.